# What sort of maths is this?

I have a number n

I increase n. I now have a new number n+1

I change my mind and decrease n: I now have a new number n-1

I change my mind again and increase. I am now back to n+1

No matter what I do along the above lines by increasing and decreasing, I can't get back to n.

What am I doing?

Clue

The answer may be nearer than you think

## 1 Answer

Is it:

The StackExchange vote system? If you upvote someone, he goes from 0 to 1, but if you decide to downvote him afterwards, it'll get to -1, and we can never go back to 0.

• I hope not, because you can in fact undo that. (Just click in the same place again.) – Gareth McCaughan Mar 18 '19 at 11:21
• @ Gareth McCaughan - Yes but I clearly said, "No matter what I do along the above lines". That means by performing the same set of operations. – chasly from UK Mar 18 '19 at 12:29
• @chaslyfromUK sorry, I actually didn't think this would be the answer. It's too late to edit it but I can just delete it instead. – hexomino Mar 18 '19 at 12:37
• @chaslyfromUK without your clue i don't think that I could have find the answer so quickly ;) – Rémi Henry Mar 18 '19 at 13:06
• @chaslyfromUK Does increasing twice in a row count as performing the same set of operations to return to $n$? – noedne Mar 18 '19 at 14:16